Remotely controlled flash unit



March 27, 1951 E. R. FARBER 2,546,734

REMOTELY CONTROLLED FLASH UNIT Filed March 19, 1947 Patented Mar. 27, 1951 Edward R. Farbcr, Milwaukee, Wis., assignor to Strobo Research, Milwaukee, Wis., a corporation of Wisconsin I Application March 19, 1947, SerialNo. 735,759

' 3 Claims. (01. 67-31) Thisinvention relates to improvements in re motely controlled flash units. It has particular application to the socalled slave unit employed to fire one or more flash bulbs for photographic purposes subject to remote control by radiant energy. In the preferred embodiment of the invention, the radiant energy may comprise light from a master flash unit, but the art has recognized high frequency radio waves and other forms of radiation as equivalent to radiant light energy in the operation of a slave unit. Consequently, while the present invention will be described with reference to its preferred light-operated embodimerit, it will be understood, without further mention herein, that the present invention resides in the slave unit irrespective of the form of energy by which it is controlled and, where reference is made to a photoelectric tube or cell, it is intended to include as an equivalent, apparatus appropriate for the reception and use of forms of radiant energy other than light.

' The present invention has several important objectives: In the first place, the slave unit towhich this invention preferably pertains is one rendered highly portable by the use of batteries as a source of electrical energy for its operation. A primary object of the invention is to protect and conserve thebattery both before and after the flash lamp is fired by providing means whereby, without any conscious attention on the part of the operator, the battery circuit will be open until the flash lamp is inserted in the socket and will be reopened. automatically as soon as the flash lamp fires, or at least as soon as the burned out tube is're'moved from itssocket. .The arrangement not only conserves battery energy, but also protects the apparatus, which usesa gaseous tube or thyratron as atrigger tube for releasing the energy necessary to fire the flash lamp.

The grid of a gas filled tube is able to exert control overthe flow of current only upv to the time when the tube fires. Thereafter, unless the circuit is broken elsewhere, current will continue to flow through the tube, this characteristic being particularly apparent where, as is the case in the preferred battery power apparatus, direct current is used, By the arrangement of the present inventiongwhich automatically, or without special attention, opens the circuit, the thyratron, as well as the battery, is protected against damage such as might occur if uncontrolled current flow were to. continue. I shall disclose a number of difierent, species of devices for automatically opening'the circuit either immediately upon the firing of the lamp or as a consequence. of the removal of the fired lamp from its socket.

In the second place, it is an important object of the invention to provide a slave unit for the control of a flash lamp" with means so regulating the firing of the trigger tube that it will be fired only by an extremely sharp radiant impulse. This feature of the invention has particular reference to the preferred embodiment where light is used as the radiant energy for controlling the unit. But for the regulating feature to which the present object pertains, the slave unit might be caused to operate if carried past a lamp or a window, or it might even be operated by the movement ofa shadow'with respect to its receiv; ing photocell. f I I Other objects will be more apparent from an analysis of the following disclosure of my invention. In the course of this analysis, the term flash lamp is used 'to designate any of the photoflash bulbs commonly used in photography and described, for example, in issue 28 of The Complete 7 Photographer, published June 20, 1942, by National Educational Alliance, Inc. Chicago, Illinois. Such a lamp comprises a bulb containing aluminum wire or leaf foil and oxygen. The lamp has a conventional base with a' shell and center contact connected within the bulb by a small filament covered with a primer which will flash and ignite the foil when the filament is heated by an adequate electric current. The trigger tube or thyratron may be of the type described in the publication Introduction to Electronics, Educational Bulletin No. 8, copyright 1945, by Allis Chalmers Manufacturing Co. It is a gas-filled electronic tube having a grid, a plate or anode and a hot or cold cathode. In the drawings: I Fig. 1 is a' circuit diagram of an embodiment of my invention.

Fig. 2 is a circuit diagram of a modified em bodiment of my invention. Fig. 3 is an enlarged fragmentary detail view in side elevation diagrammatically showing a lamp socket used in the device of Fig. 2. I Fig. 4 and Fig. 5, are circuit diagrams illustrating further modified embodiments of my invention. I Since the underlying purpose of providing a self-contained slave flash unit is to have such a unit which is small, compact and lightin Weight, the construction shown in Fig. 1 isoften preferred because of its simplicity. There is a socket element 6 screw-threaded to. receive the conventional shell 1 of the base of theflash '2 a) lamp 8. The socket is provided with the conventional insulation at 9 for the center contact l with which the central electrode of the lamp engages when the lamp is in place in the socket as shown.

, The central contact H1 is connected by conductors H, I2, 3 with one side of a condenser l4 which, ;for example, may have a capacity of 8 mid. The other side of the condenser is com nected by conductors l5, it through resistance l1 and conductor [8 with battery IS. The resistance I! may have a value on the order of 50,000 ohms. The battery ll! preferably has its positive terminal connected with resistance and may be capable of supplying 9K) to 135 volts. negative side of the battery connects through conductor 20, normally closed switch 2i, and conductor 22 with the socket shell 6.

Another switch, 23, normally open, may shunted across the socket.

The photocell 25 and resistance at are connected in series by conductors 21, '28, 29 across the condenser i l. Likewise connected across condenser I4 is the trigger tube or thyratron 30, whose anode 3! is connected by conductor 32 to conductor 15 and whose cathode 33 is connected by conductor 34 to conductor 2!]. The grid 35 of the thyratron trigger tube is connected by conductor 36 and conductor 31 through a condenser 38 to conductor 28 which intervenes between the photo-electric tube 25 and the resistance 26. The condenser 38 preferably has a value of approximately .002 mid. This value is fairly critical, whereas the values of the other elements above described are rather uncritical. I find with regard to condenser .38 that a value bf .05 is too large, allowing slow variations of light intensity to tripthe thyratron, and a value or 40005 is too small, although earlier photoflash lamps have steep enough curves to operate a thyratron even with a condenser as small as .0905. For the photoflash lamps currently in use, therefore, the condenser shown at 38 should preferably have a capacity between .007 mid. and .O i mid, a capacity of .002 mfd. being right.

It will be noted to be a feature of the embodiment above described that there are two separate circuits, both of which are connected through the socket for the flash bulb. One of these is the battery circuit to the condenser and the other is the circuit by means or" which the corn denser is discharged to flash the bulb. v

The high resistance at H positively precludes any flow of battery current through the thyratron trigger tube 30. However, it would permitflow of battery current slowly through the photoelectric cell 25 but for the fact that when there iskno flash bulb in the socket, the circuit through thephotocell 25 from battery [9 isopen.

The act of inserting the flash bulb 8 in the socket closes through the filament of the bulb a circuit between the socket shell 6 and center contact Ill- This permits the battery to charge thelcondenser at M. The resistance-at ll 'pre eludes any flow of current heavy enough to heat the filament of the flash bulb to the firing point,

while still permitting a trickle charge into the condenser.

When the condenser is charged, any light fallon the photocell 25 will tend to establish a flow" of current between the electrodes of that. cell. When the light falling on the cell is sharply. varied, the resulting impulse will tend to fire the thyratron trigger, tube 30, but if the impulse is not too rapid, it will-bleed off through the l?eslstance 26. This eliminates the danger that the flash tube 8 may be fired prematurely by the light and shadow of persons passing the photocell, or by carrying the portable slave unit past an open window. However, when the light of the flash of a master unit falls on the photocell, the energy impulse is so abrupt as to create a current incapable of bleeding off through the resistance 26 but of sufficiently high frequency to traverse readily the condenser 38 to the grid 35. This ionizes the gas of the thyratron trigger tube. The condenser M thereupon discharges through such tube and through the filament of flash bulb 8 to fire the flash bulb.

high resistance at I? causes th thyratron to extinguish itself immediately when the current from the condenser has been discharged. The burning out of the filament of flash bulb t has reopened the circuit between the battery; and the condenser and betweenthe battery and the photo-electric cell. Thus, the battery isauto matically protected against any further discharge whatever. I

The switches shown at 2! and 23 are safety switches. Opening the switch at 21 or closing that at 23 will, in either case, prevent the acci-1 dental firing of the photo-tube while the operator still has it in his hand. Either of these switches may be used alone, but both may be present in the circuit if desired. The diiierence between them lies in the fact that it is sometimes desirable to set the slave unit in operation with a minimum of time lost and, on such occasions, it is desirable to uses. switch located as at 23 so that the closing of the switch. will not only short circuit, and thereby: protect, the flash bulb, "but will permit the starting of the charging of the condenser The values of the condenser and the battery and the thyratron are related. If the trigger tube has a high voltage drop, the voltage of the battery will have to be high. The energy storage in the condenser it must be great enough to fire the flash lamp, but its actual size will depend on the voltage of the battery and the voltage drop of the thyratron.

In the embodiment just disclosed, the thyra tron trigger tube was shown using a cold cathode. Ahot cathode trigger tube may also be used and a disclosure of such a tube is made in Fig. 2; Fig. 2 further modifies the arrangement shown in Fig. 1. In Fig. 2, as in Fig. 1, the insertion of the flash bulb closes the circuit but this is done ina difierent manner in Fig. 2 and one result of the modified arrangement lies in the fact that the reopening of the circuit depends, not upon the of the flash bulb, but upon its withdrawal from the socket.

Fundamentally, the circuit of Fig. 2 is very similar to that of Fig. 1. There is a battery at I99 connected by conductor [8 with a resistance ll" which may be assumed to be identical with that of Fig. 1. Thence the same conductors I6, I5 lead to the condenser here designated 140. The photocell 25 and resistor 26 are connected acrosscondenser Hill by conductors 21, 28, 29, l 3, exactly as in Fig. 1. From a point between the-photocell 25 and resistance 25, conductor 31 leads to con: denser 38, which isconnected by conducto rYiiii with the grid 35a of a hot cathode thyratron trigg'er tube 300. The anode 3| is connected bycon-L ductor 32 to conductor 15. The cathode 33B is. connected by conductor 340 to the central contact I00 of a special split socket shown in detail Fig. 3, The shell of the socket is dividedinto,

component parts" 600, 60] which "are insulated by spacing them apart, thethreads of one element being complementary tothe threads of the other so that the base of the flash bulb 8 may be screwed into the socket exactly as if the elements 600, Bill were integral. V

One of the socket shell elements 600 is connected by conductor 220 and conductor 200 to the battery I90. The other socketshellelement GUI is connected by conductor III! to the positive terminal of a filament heating battery 40, the negative terminal of which .is connected by conductor 4| with the filament 42 which heats the cathode 330 of the thyratron trigger tube 300. The otherv side of the'filament'is connected by conductor 43 through a thyrite resistance 44 and conductor 45 to the'conductor 22S and thence through the'normally'open' socket circuit back to the filament heating battery 40. A normally open safety switch 46 is shunted between conductor 43 and conductor I I 0 across the resistance 44 and the normally open socket to close the filament heating circuit. In order to keep the grid 350 normally negative, I may connect the grid resistor 47 between the grid and the negative side of battery 4B. This is done by conductor 36, conductor 48 and conductor 49.

The grid resistor 41 may have a value of meg. The battery I90 may be 45 to 90 volts. The condenser I 40 may have a capacity of 1 mfd. The

filament battery 40 may be a six volt battery. The resistance I! may be 50 000 ohms as already described: The condenser 33 is preferably .02 mfd. and must be within the approximate range already described. The resistor 26 may be meg. as already described, or may be as small as 10 meg. if desired. The thyrite resistor at 44 is a type of resistance which decreases rapidly as the applied voltage rises. It is intended to bypass any voltage surge.

In general, this circuit operates in much the same manner as that shown in Fig. 1. Specifically, the control circuit does not need to be completed through the filament of flash bulb 8, but is completed circumferentially of the base of the bulb between the component socket shell parts 600, 60!, when the bulb is inserted in the socket. Insertion of the bulb closes the filament heating circuit and enables the current from the filament battery 49 to heat the filament 42. Insertion of the bulb also closes the circuit which enables the battery I85 to charge the condenser I49. Both of these circuits are completed through the shell portions of the bulb base without involving any interior circuit through the flash bulb itself. Additionally, as will be obvious, the insertion of the bulb in the socket further completes the firing circuit between the central electrode of the bulb base and the central contact Iefi of the socket, this circuit including the anode and cathode of the trigger tube and the storage condenser I40.

The actual firing of the trigger tube and flash bulb occurs as already described, when energy radiation is received in such intensity that it cannot leak ofi through resistor '26 and will pass condenser 38 to affect the grid s.

The firing of the flash bulb still leaves the filament heating circuit closed cii -.ierentially of the bulb base, but the removal c the bulb from the socket reopens all circuits."

Fig. 4 shows a simplified version of the embodiment of Fig. 2, requiring no storage condenser. The battery I9! is relied upon to supply all energy required to fire the trigger tube 390. To protect the thyratron from continued high current flow in the case of defective orgshorted lamps, a fuse 56 is used. The circuit demonstrates that the resistor I1 and various other components may be eliminated.

The embodiment shown in the circuit of Fig. -5 is similar to that at Fig. 1 in that the current which affects the control of the apparatus flows through the filament of the flash bulb 8. In this instance, the insertion of the bulb closes a circuit between a relay battery 55 and a relay winding 56 to close relay switches 51, 58. The closin of switch 58 enables the battery 55 to energize the filament 42 for heating the hot cathode 338. The closing of switch 51 is also essential to complete the filament circuit, but it is also essential to connect the flash bulb 8 operatively across the condenser I4I. In this instance, the condenser is so disposed as to be permanently charged by the battery I 9| at the moment following discharge through the flash bulb. The condenser portion is interchangeable as between the arrangement shown in Figs. 1 and 5, that shown in Fig. 1 being preferred for reasons already described and that shown in Fig. 5 being merely illustrative of a possibility within the scope of the invention. So far as the relay is concerned, it will be obvious to those skilled in the art that this circuit is fully equivalent to that shown in Fig. 1, inasmuch as it mererly does through a relay what Fig. 1 accomplishes by direct connection. In both instances, the battery circuit for possible discharge through the photo-electric cell is opened automatically by the firing of the bulb. The circuit remains open until a new bulb is inserted, thereby energizing the filament of the thyratron and completing the battery circuit through the photocell.

While, as above stated, the invention preferably finds its embodiment in a slave unit for photoflash purposes, it will be apparent that many of the features of my invention are of general application in other slave units, wherever any actuated device requiring a predetermined value for its operation may, merely by being connected into the circuit, pass suflicient current through a secondary circuit for control purposes.

I claim:

1. In a flash-bulb firing system, a capacitance, a charging circuit comprising a voltage source in series with the capacitance, a discharging circuit, comprising a firing switch means and at least two terminals in series with the capacitance, the terminals being adapted for connection to the igniting element of a flash-bulb, a control circuit for controlling the firing switch m ans comp-rising a radiant energy responsive means in series with the voltage source, and circuit closing means in the said control circuit, the circuit closing means comprising means to complete the control circuit only when a flashbulb is connected with at least one of the said terminals, whereby current drain through the control circuit is prevented when no flash-bulb is connected to the said one terminal.

2. In a flash-bulb firing system, a capacitance, a charging circuit comprising a voltage source and at least two terminals in series with the capacitance, a discharging circuit comprising a firing switch means and the said terminals in series with the capacitance, the terminals being adapted for connection to the igniting element of a flash-bulb, a control circuit for controlling the firing switch means comprising a radiant energy responsive means in series with the voltage source, and circuit closing means in the control circuit, the circuit closing means comprising means to complete the control circuit only when a flash bulb :is connected with at least one of the said terminals, whereby current drain through the control circuit is prevented when no flash-bulb is connected to the said one terminai.

3. In a flash-bulb firing system, a capacitance, a charging circuit comprising a voltage source and at least two terminals in series with the capacitance, a discharging circuit comprising a firing switch means and the said terminals in series with the capacitance, the terminals being adapted for connection to the igniting element of :a flash-bulb, a control circuit for controlling the firing switch means comprising a radiant energy responsive means in series with the voltage source, and circuit closing means in the con- 8 oral-circuit, the circuit closing means comprw ing' the said two terminals, whereby all mn'went drain is prevented when no circuit be; tween the-said terminals. j

REFERENCES CITED The following references are of record in the file "of this patent: n v

UNITED STATES PATENTS Blair Dec. e. 1942 

